The invention relates generally to the field of electrical power converters and inverters. More particularly, the invention relates to techniques for verifying that a disable circuitry of a power converter or inverter is functioning properly.
Power inverters and converters typically employ power modules to create a desired output voltage waveform, which is used to power various devices, such as motors and other equipment. The frequency and amplitude of the output waveform may affect the operation of the device such as by changing the speed or torque of a motor, for example. Some power modules create the desired output waveform through pulse width modulation, wherein power semiconductor switches such as insulated gate bipolar transistors (IGBTs) are caused to switch rapidly on and off in a particular sequence so as to create an approximately sinusoidal output waveform.
In certain circumstances it may be necessary to disable the power module. Therefore a variety of methods exist for powering down power modules, depending on the level of disruption that may be considered acceptable under the circumstances. For example, in some cases, it may be sufficient to simply decouple the power module from its power source. However, doing so may also power down other power module circuitry that may be useful even though power is not being delivered to the load. Furthermore, the time and effort used to bring the power module back to a fully operational state may be extensive. Therefore, it may be useful in some circumstances to disable certain circuitry within the power module that will prevent the power module from outputting power to the load while maintaining the operability of certain monitoring and control functions. In this way, useful functions of the power module be used while the output power to the load is disabled. Additionally, the power module may be brought back to a fully operational state more quickly if only a portion of the circuitry is disabled.
In cases where only a portion of the power module circuitry will be disabled, techniques are usually employed to ensure that the shutdown circuitry will operate properly when engaged. For example, a verification circuit may be used to periodically test the shutdown circuitry. The shutdown test may, however, tend to stress the power module circuitry or the load device, possibly leading to device failure.
To meet some industry requirements for circuitry designed to shut down motor drives and other power equipment, the ability to test the shut-down capabilities of the disabling equipment may be required. For example, to comply with what are currently the most stringent requirements, the disabling circuitry must be capable of demonstrating its ability to shut down power to loads during real time operation of the equipment. Here again, however, such actual loss of power can perturb production equipment, and degrade the equipment. For pulsed motor drives, for example, rapid interruption and re-initiation of a pulse train powering the load can cause high potential differences within and between phase conductors that can lead to degradation of insulating systems, and eventually to failure of the motor or other system component.
It may be advantageous, therefore, to provide a system and method of testing a shutdown circuitry that is less disruptive of the normal operation of the power module.